We propose continuation of a National Resource dedicated to the technological development and application of Magnetic Resonance Microscopy (MRM). This Center for In Vivo Microscopy will enable investigators to noninvasively follow disease and therapies in small animal models, and 3D morphology in fixed tissues down to the physical limits of the technique (1-10 micromoles). Core research will focus on five technological areas: (a) rf probes, including a high-temperature superconducting probe that will allow experimental verification of the theoretical resolution limits in MRM; (b) projection pulse sequences and reconstructions for 3D arrays (to 1024-3) directed at the unique problems in using high-field (7-9.4 T) systems using the strong gradients required in MRM; (c) rf pulses and sequences unique for MRM; and (d) new techniques for measuring and minimizing motion in small animals to provide stable models for MRM. Collaboration will include projects to (a) experimentally determine the resolution limits in MRM; (b) connect structure and function in transgenic mouse embryos; (c) perform in vivo histology of toxic injury; (d) allow in vivo measure of glutamate concentrations in stroke; (e) study cortical architecture in the live rat; (f) follow lung injury in vivo at the alveolar level; and (g) define the impact of infarct morphology on cardiac arrhythmias. Our training program will support a diverse group of students: (a) undergraduate engineers; (b) medical students; (c) graduate students in biomedical engineering and physics; and (d) residents pursuing academic careers. Service will continue for researchers in fields from anatomy to zoology studying both live and fixed specimens in 3D with resolution less than 10 micromoles. We will exploit the growing field of multimedia to disseminate results on CD and video to the widest possible group of researchers.